I. Field
The present invention relates to the field of communications. More particularly, the present invention relates to a novel and improved method and apparatus in a code division multiple access communication system for fast processing of a transmit signal.
II. Background
Efficient processing of a signal for transmission from a transmitter is one of the sought after performance enhancements in communication systems, such as code division multiple access (CDMA) communication systems. Several of such CDMA communication systems are well known. One of the systems is the CDMA communication system operating based on the TIA/EIA-95 standard, commonly known as IS-95 standard, incorporated by reference herein. The IS-95 standard provides description and the operational requirements for the structure of transmit channels, such as the forward channels. The forward channels are directed from a base station to one or more mobile stations.
Generally, the structure of the forward channels according to the IS-95 standard requires using binary phase shift-keying (BPSK) data modulation and binary pseudo noise (PN) spreading. The data bits after channel encoding are modulated through a BPSK modulator, and a binary PN spreading/modulator spreads the BPSK modulated data symbols by inputting one symbol at a time. The binary PN spreading in this case includes two paths for the in-phase and quadrature-phase modulations. The results of each path pass through carrier modulation. After summing the carrier modulated signals from each path, the summed results are amplified for transmission from an antenna system. Specific requirements for the IS-95 forward channel structure are described in section 7 of the IS-95 standard.
A communication system defined and operated according to the TIA/EIA/IS-2000, commonly known as the IS-2000 standard, incorporated by reference herein, also includes a forward channel structure. The IS-2000 forward channel structure is defined in section 3 of the standard. The IS-2000 system is backward compatible to the IS-95 system. On the forward channel, in addition to the requirement for BPSK modulation for IS-95 compatibility, IS-2000 systems require QPSK pre-spreading of the data symbols. For QPSK spreading/modulating, the input section of the modulator requires two data symbols at the same time, namely in-phase and quadrature-phase data symbols.
In such systems, there is a need for efficient processing of signals to save processing time and reduce cost. Additionally, there is a greater advantage to provide a method and apparatus for efficient processing of data symbols in a transmitter for transmitting forward channel signals in a CDMA communication system.
The presently disclosed method and apparatus are directed for efficient processing of signals in a communication system. In-phase and quad-phase data symbols are produced after an encoding process to facilitate efficient processing of a signal. Partitioning a RAM structure facilitates production of in-phase and quad-phase data symbols simultaneously. At least two scramblers are used to receive and scramble simultaneously the in-phase and quad-phase data symbols. A Walsh covering/summing block provides efficient Walsh covering and summing of signals for a combined transmission from the communication system.